When the hand brake is disengaged on my 1953 XK120M, the nut on the end of the bolt for the clamp connecting the cable mount bracket to the shaft attached to the hand brake lever hits a small oval plate on the drive shaft. I’m not sure if the clamp has slipped on the shaft or if the plate on the driveshaft is even supposed to be there. The hand brake diagram in the service manual shows this bolt in a position parallel to the drive shaft, but it’s not clear if that is in the engaged or disengaged position. Can someone tell me what position this bolt is supposed to be in when disengaged?
I’m fairly certain the plate on the drive shaft is not original to the car. It might have been added later to balance the shaft, though I don’t know why this would be necessary. Does anyone else have a similar plate on their drive shaft? Without this plate, the bolt would not contact the drive shaft, but would still be within 2 or 3 mm.
On my XK120, the clamp bolt is parallel to the driveshaft. Thus, the clamp bolt never comes within one inch or so of the driveshaft. My driveshaft also has the circular plate, so it appears your driveshaft is original.
Good diagrams of the handbrake mechanism are shown on pages 127 and 128 of “Jaguar XK120 Explored”. Looking at those diagrams, I’m guessing that the clamp is 90 degrees off, from where it should be, on the shaft. I’m not sure how this could happen as both the clamp and the handbrake operating lever are supposed to be keyed to the shaft. One or both keys may be missing on your shaft.
Mine also has an oval balancing plate. I imagine they came in different sizes as needed.
Both clamp parts are woodruff keyed to the shaft.
Notice the hole in the chassis for the adjuster to pass through.
Is there any chance your gearbox mount is going bad, allowing the tail end to sag?
Thank you for the responses. I suspect now that the balancing plate is original to the car,which means it isn’t the source of the problem. I hadn’t considered that the gearbox mount could be a problem, so I’ll need to look further into that. How can you tell if the mounts are going bad? I’ve included a picture of mine.
I don’t have the book Mike refers to, but looking at the service manual and Rob’s pictures, the clamps look correctly positioned relative to each other and they are solidly in place, so I think the keys are ok. However, the bolt nearest the prop shaft appears to be more inclined toward the shaft on mine than it is on Rob’s car. Then again, this could be an optical illusion due to the different shafts. The angles of the bolts relative to the hand brake adjustment appear about the same. My car has the longer prop shaft.
Porter notes in Original Jaguar XK that the longer prop shaft was adopted in February 1952, along with a short mainshaft gearbox without rear extension (Clausager, XK120 In Detail, puts the change in January 1952).
On the longer prop shaft, the larger diameter piece runs from the U-joint at the rear axle, extending above the hand brake mechanism, almost to the trailing edge of the cross member. It’s clear that the longer shaft does not give the same clearance to the hand brake as the earlier shaft did. I’ve included a picture below, in which you can see the groove cut into the balancing plate on my prop shaft caused by the nut hitting it. Note the angle of the bolts on the mechanism in comparison to the same in Rob’s picture, and that the hand brake levers are both in about the same position (disengaged).
The bolt on mine appears to be in backwards which would steal a mm or two of clearance, though not enough to completely solve the problem when I reverse it. So it might me the gearbox mounts, combined with the backwards bolt.
Your photos seem to confirm that the woodruff keys are not missing from either the center clamp or the handbrake lever. Your photos seem to show that the center clamp and the hand brake lever are aligned on the shaft in the same positions as they are on Rob Reilly’s and on my XK120.
I got under my car with a calipers to measure the closest distance between the nut on the upper bolt and the oval balance plate when the handbrake is in the released position. It’s right at 3/4 inch. Looking at your photos, it appears that your handbrake mechanism is assembled correctly. Thus, I agree with Rob’s observation that the rear of the gearbox is too low bringing the oval balance plate into contact with the nut on the upper bolt.
You presumably have the short tail JL gearbox where I have the JH with the long tail.
But there shouldn’t be any difference in position.
I see you are missing the C4476 shield, but that is only a thin piece of sheet steel so it wouldn’t make that much difference.
Looking in the parts catalogue Engine Block Section, I see C.4308 Carrier Bracket for rear mountings, which you have, that’s the saddle shaped plate above the rubber discs. But what is something called C.5805 Bracket Assy for rear mountings? I see only one item on yours. Is something missing? Or is C.5805 the bracket with the two gussets welded to the chassis?
Viart page 102 does not give a part number to this later bracket.
In any case, you could raise up the tail with some washers.
In Rob’s picture I can see that his sliding yoke is at the forward end of the D/S. In your pictures it isn’t clear if your yoke is at the front or the rear.
Nick appears to have a later XK120 with the JL series gearbox and longer driveshaft. The sliding yoke is just an inch or two forward of the oval balance plate shown in Nick’s first photo.
Correct. I believe the car was manufactured in late 1952, (Chassis # S 673080) but haven’t confirmed that. It does have the later drive shaft.
Feeling a bit foolish, but after some thought it dawned on me that, having the car up on jack stands, the rear suspension was fully extended, thereby increasing the angle of the prop shaft relative to the gearbox and decreasing the distance to the handbrake mechanism accordingly. With the car back on level ground, I measured the gap again and found it to be 5/8 inch from the nut to the shaft without the balancing plate and just over 1/4 inch to the plate itself. 5/8 inch doesn’t sound much different from the 3/4 inch you measured, but it’s hard to believe that Jaguar would have left just 1/4 clearance to the plate. As demonstrated, this would allow the shaft to rub on the nut if the rear suspension comes close enough to the stops (C.632). Could the rubber buffers (C. 632) be worn or compressed, allowing more than normal rear suspension travel?
I’d still like to find out if the gearbox is being held at the proper height. I measured it with a caliper at 1 and 86/1000 inch from the “V” type bracket on the chassis to the adaptor plate (C.5805) at the edge of both and 1 and 11/1000 inch at the hole in the chassis bracket. Both measurements are from the bottom of the adaptor to the bottom of the chassis bracket. Is there a specification for this distance?
I’ll add that the drawing of C. 632 on page 400 of Viart’s book (of which I now have a copy) shows a flat surface at the top of the buffer, but mine do seem to be somewhat dished in the middle where the axle would make contact - and apparently has.
According to Porter’s Original XK 2nd ed., 673080 would have been finished in Oct '52.
There isn’t really a spec that we have access to for chassis parts such as these, short of the factory releasing their engineering drawings, but you might look at the C.4304 rubber bobbins which could be starting to squish out. If you want to raise the gearbox you could put some washers between it and the C.5805 adapter plate.
Take a look at Viart page 127 and see if your hand brake mechanism looks like his drawing.
The C.632 buffers get dished from leaving the car on stands with the axle dangling for long periods, but should not cause this driveshaft clearance problem.
Looking at it another way, could the front of the engine be too high?
